1. Field of the Invention
The present invention relates to a pressure switch, which outputs a detection signal when the pressure value of a pressure fluid, as detected by a detector, matches and agrees with a preset pressure value.
2. Description of the Related Art
Heretofore, transporting a workpiece to a predetermined position has been carried out by supplying a negative pressure fluid to a suction transport means made up, for example, from a suction pad, and while the workpiece is attracted under suction to the suction pad. In this case, in order to confirm whether or not the pressure value of the negative pressure fluid supplied to the suction pad reaches and attains a predetermined pressure, whereby it can be confirmed whether or not the workpiece has been reliably attracted under suction, a pressure switch is employed. Generally speaking, such a pressure switch is equipped with a semiconductor pressure sensor functioning as a detector, whereby the pressure of the fluid is detected based on a resistance value that changes in accordance with the pressure imposed on the pressure sensor. In addition, in the case that the pressure value detected by the pressure sensor agrees with a preset pressure value that is set beforehand, it is judged that the workpiece has been attracted under suction and a detection signal is output.
As disclosed in Japanese Laid-Open Patent Publication No. 7-37473, in this type of pressure switch, a vacuum piping is detachably connected through a pipe coupling to a pressure intake of a main body in which the detector is accommodated. The negative pressure fluid that flows through the vacuum piping is introduced into the main body, whereby the pressure of the negative pressure fluid is detected.
However, with the aforementioned pressure switch, oil droplets that are ejected from the compressor making up the source of negative pressure, or water droplets generated due to condensation as well as foreign matter contained within the fluid, move along the vacuum piping and collide against the pressure sensor, which is accommodated inside the main body. In this case, because the pressure sensor is constructed such that the pressure of a fluid that flows through a very small opening arranged within the flow passage is detected, the oil droplets, water droplets and foreign matter flow through the small opening and impinge directly on the pressure sensor. Thus, defects are produced in the pressure sensor, raising concerns that the detection accuracy will become deteriorated.